A Police officer cannot as a rule give evidence of opinion except in a couple of circumstances, the first being the opinion that someone was/is drunk and the second is for excess speed, where a Traffic officer is deemed an exert and is allowed to give the opinion that someone was speeding but this is then usually corroborated by a device such as a calibrated speedometer in a following check (over 1 mile on a motorway or 3/10 of a mile on all other roads)
VASCAR which measures time over distance and gives an average speed, Lazer which provides an exact speed, and Truvello which is the 2 cables placed across the carriageway 1.85 meters apart.
When it comes to using a mobile phone it has always been deemed (as for 99% of offences) that the Police would only stop and report a driver for offences if
1. The officer has seen the commission of the offence
2. The officer is satisfied that there is sufficient evidence to prosecute for the offence
Bear in mind that the use of the mobile phone only applies to using a hand held device (Bluetooth and hands free are still legal), and the loopholes, (which I can explain if wanted) were removed in 2022.
Always bear in mind that the Police do have the power (as happens in any crash where an allegation or belief that a phone was used at the time) to request the phone records of that individual just as the alleged offended can use his/her phone records to prove that they were not on the phone at the alleged time, so it works both ways.
So this is why a Police officers word is usually sufficient backed up by contemporaneous notes (often a FPN or Offence report HO/RT10) and the courts will usually take the officer at his word unless evidence is produced to the contrary or it is contradicted by some hard contrary evidence.
That having been said, I would be kidding myself if I said that there are some coppers who are not honest, and that applies to all walks of life, but in the majority of cases most coppers will do the job to the best of their ability and honestly but mistakes also get made.
With a phone offence though, it is too much of a minor offence to drop yourself in the sh!t and the courts will still take coppers at their word especially as a case can be proved or disproved by production of the phone records.
This is why drivers (or anyone alleged to have committed an offence for that matter) have the right to plead not guilty (even if given a FPN) and go to court to argue your case before the courts.
I lost count of the number of people I booked for using and held devices, and always remember if a crash or other incident occurs (even using Bluetooth) could result in a prosecution for dangerous driving or careless driving and in the case of a fatality (again which I have dealt with many) a prosecution for causing death by dangerous driving.
In conclusion, most offences have the evidence corroborated by evidence or witnesses, but traffic offences are still prosecuted in the main on the trust of the Police by the courts with only a few (as I have explained) requiring corroboration, but even then much is backed up these days n-by on board cameras although these are mainly only fitted to Traffic cars as Panda car drivers have to jump through hoops to do anyone for speed offences.
